1. Field of the Invention
The present invention relates to antennas for use in a wireless communications systems and, more particularly, to a simplified traffic matrix for balancing wireless traffic at an antenna station.
2. Description of the Background
Typical wireless systems divide geographical areas into a plurality of adjoining cells, and each cell is provided with a wireless cell tower. The frequency band within which wireless radio systems operate is limited in band width, and so available carrier frequencies must be used efficiently in order to provide sufficient user capacity in the system.
One solution to increase call carrying capacity is to create more cells of smaller area, and/or add more carriers to existing cells. However, creation of new cells involves increased equipment and real estate procurement costs for more sites. This can be an unduly expensive proposition. It can be far more economical to solve the problem with better antennas and traffic management.
Typical existing systems increase carrying capacity through the addition of digital carriers. For this, each cell is sectorized into nominal 120 degree angular sectors. Each 120 degree sector is served by multiple antenna elements spaced apart from each other. The use of multiple antennas is known as “diversity” and it solves the problem wherein a given antenna does cannot always see its intended signal (such as around high-rise buildings). A diversity antenna array helps to increase coverage as well as to overcome fading. When one antenna is fading and receiving a weak signal, another of the antennas is receiving a stronger signal. For example, on a typical uplink each antenna has a 120 degree wide beam of high gain sensitivity from which it picks up signals from mobile stations within a zone covered by the beam. The coverage of antenna elements overlap, so that a signal transmitted by a mobile station (MS) within a zone may be received by two or more antenna elements. Multiple antennas ensure the integrity of the transmission and reception.
“Beam shaping” is another tactic used in diversity antenna arrays which allows operators to optimize capacity, providing the most available carrier frequencies in sectors which need it most. User demographics may change to the point where the base transceiver stations have insufficient capacity to deal with demand from a localized area. For example, a new housing development within a cell may increase demand within that specific area. Beam shaping can solve this problem by distributing the traffic among the transceivers.
Prior art beam shaping solutions utilize complex beam-forming devices (LPAs, controllable phase shifters, etc.), many of which are not well suited for deployment at a masthead or tower-top with an antenna array. For example, existing adaptive arrays provide steerable antenna beams that may be controlled to individually point at a current mobile position, and these can be used to customize coverage within a cell to avoid the disadvantages associated with fixed antenna beams. ArrayComm is marketing its adaptive array antennas for use over Personal Handyphone System (PHS) networks in Asia and Latin America. Metawave is also selling beam-switching antennas for use over AMPS and CDMA networks. Metawave's SpotLight® system intelligently switches between 12 directional antennas -- each with a fixed, 30-degree beam. However, this use of computer-driven adaptive array antennas generally requires the real time determination of complex traffic weighting information (to determine demand within the area of coverage of the cell tower) as well as a plan to allocate the traffic among the available antenna transmitters/receivers. The determination of such weighting information and its use generally requires substantial processing resources to provide real time antenna beam steering and can result in signal processing delays or other undesired consequences. Other beam-forming devices use RF switches, LPA phase shifters, and complex software to form a beam that an operator pre-selects. All such highly-complex equipment is very prone to failure, a intolerant situation for wireless providers.
It would be much more desirable to eliminate the processing overhead and provide a means to allow manual sculpting of the beams to accommodate demographic or other changes. Accordingly, a need in the art exists for a system and method adapted to control the transmission and/or reception of signals that avoids the need for intensive processing capability in beam forming.